The present invention relates to a method for determining a network access address for transmitting messages from a switching system to a communication terminal which is connected to the switching system via a communication network.
As a rule, the subscriber number allocated to a subscriber, e.g. the telephone number, or the fax number is established by the association of the communication terminal allocated to the subscriber with a switching system in communication landline networks.
The subscriber number (e.g., 636-82963) is composed of a part identifying the switching system (e.g., 636) and a part identifying the subscriber (e.g., 82963), the latter being determined by the subscriber interface of the switching system via which the communication terminal is connected to the switching system.
When the subscriber moves, the subscriber number allocated to the subscriber usually changes, in contrast to mobile radio networks, since the communication terminal is either allocated to another switching system or the communication terminal is connected to the same switching system via a different subscriber interface.
From German Offenlegungschrift DE 196 04 244 A1, a communication system is known in which the communication terminals allocated to a switching system are connected to the switching system via an ATM-based communication network. In this arrangement, the subscriber interfaces are provided by a number of ATM hubs connected to the ATM-based network. The switching system and the ATM hub in each case have an ATM interface unit via which, on the one hand, a connection to the ATM-based network is implemented and, on the other hand, a bidirectional conversion between the internal data format of the switching system or the ATM hubs, respectively, and the ATM-based data format is effected.
In the cell-based data transmission method known as asynchronous transfer mode (ATM), fixed-length data packets, so-called ATM cells, are used for the data transport. An ATM cell is composed of a five-byte-long header containing switching data relevant to the transport of an ATM cell, and a forty-eight-byte-long payload.
Data transmission via an ATM-based network generally takes place in so-called virtual paths or virtual channels. For this purpose, interconnection tables with switching information consisting of a virtual channel identifier and of a virtual path identifier are set up in the respective ATM network nodes by an exchange of signaling information during a connection set-up before the beginning of the user data transmission. In the interconnection tables, a so-called VCI value is assigned to the virtual channel identifier and a so-called VPI value is assigned to the virtual path identifier. The switching information entered in the interconnection tables establishes how the virtual paths or, respectively, virtual channels contained in the virtual paths of the incoming and outgoing connections at the ATM network node are correlated with one another by the signaling; that is, which input is connected to which output by switching. ATM cells transmitted via these virtual connections have switching data essentially consisting of a VPI value and a VCI value in the header. The ATM header data is processed, i.e. the switching data arranged therein is detected and evaluated, at the input of an ATM network node. The ATM cells are then switched through by the ATM network node to an output representing a certain destination via the switching information stored in the interconnection table.
For addressing a subscriber interface of the ATM hub or a communication terminal connected to the subscriber interface via the ATM-based network via the switching system, an ATM channel is set up for each communication terminal between the ATM hub and the switching system, i.e. an unambiguous VPI/VCI address is allocated by the switching system to each subscriber interface of an ATM hub or, respectively, each communication terminal connected to a subscriber interface, for a data transmission. The VPI/VCI address has hitherto been allocated to the respective subscriber interfaces and administered manually in the switching system.
If the allocation of a communication terminal, allocated to the communication system, to a subscriber interface of an ATM hub is changed, i.e. because of a move, but the call number of the communication terminal is to be retained, a manual change of the VPI/VCI address allocated to the communication terminal is necessary in the switching system. However, this is very complex, especially in large communication systems.
The present invention is therefore directed to a method via which a network access address can be automatically allocated to a communication terminal in a simple manner.